This invention relates generally to component feeding systems, and moir particularly to a system for slitting a cover tape in a tape-based component feeding systems used in conjunction with surface-mount or equivalent automated assembly systems.
The present invention is directed to an improvement of tape or component feeders used in surface mount assembly technology in which electronic components are placed at precise locations on the surface of a printed circuit board. As illustrated by the Hover-Davis MPF and QP2F products, component tape feeders are used for sequentially feeding surface-mount components to a host assembly system. The host system typically includes a pick-and-place machine having an automated or robotic head for retrieving the component from the component feeder and placing the component on the surface of a printed circuit board that is being assembled.
For ease of assembly and use, components are often stored in a carrier tape as depicted in Prior Art FIG. 1. Carrier tape 30, consists of a flexible base 32 of paper or plastic having depressions 34 at regular intervals along its length. Carried within each depression is one component 36 to be placed on the printed circuit board. The components 36 are secured within their respective depressions using a thin transparent material 40, commonly referred to as xe2x80x9ccover tapexe2x80x9d or xe2x80x9ccover layerxe2x80x9d that extends the length of the carrier tape, and is generally slightly wider than the depressions that it covers. The cover layer is typically fastened to the carrier tape with a pressure or temperature activated adhesive along each of its two longitudinal edges. The carrier tape also includes a plurality of through-holes 42 spaced at a predefined pitch, wherein a drive mechanism is able to engage the holes and advance the tape at a controlled rate/distance in order to accurately present the components to the pick-up location.
In component tape feeders, such as the Hover-Davis models noted above, a tape feeder advances the carrier tape to position a depression, and the component within the depression, at a predetermined pick-up point, where the host pick and place assembly machine is able to retrieve the component for placement on the printed circuit board. As the carrier tape is advanced off of a supply reel, the cover layer is typically pulled or peeled back from the carrier tape, just before the pick-up point, and wound upon a cover layer take-up reel, thereby exposing the depression 34 and the component 36 just before it reaches the pick-up point.
A long-standing problem with this technology has been the disposition of the cover tape. Two main methods are in use for dealing with the problem. The first is to wind the cover tape on a take-up reel located above and behind the pick point.
Examples of patents in which this solution is employed include U.S. Pat. Nos. 4,327,482; 4,735,341; and 5,299,902,
the teachings of which are hereby incorporated by reference. A problem with this method is that in order for the take-up reel to be reused, the cover tape has to be manually unwound therefrom. In addition, the cover tape must initially be threaded, or otherwise attached, to the take-up reel for the winding of the cover tape around the reel to occur. This is often accomplished with adhesive tape (e.g., masking or splicing tape) and also requires that tape be readily available when starting a new take-up reel for the carrier tape. However, attachment requires that a sufficient quantity of the cover tape be available to reach the take-up reel and attach thereto often resulting in wasted components. Furthermore, xe2x80x9cthreadingxe2x80x9d the take-up reel interrupts the assembly process, resulting in significant loss in productivity for cover tape threading, disposal, etc.
A second method of handling the cover tape after it is peeled back from the carrier tape involves using a pair of pinch rollers to push the cover tape into a disposal bin. U.S. Pat. No. 5,725,140 to Weber et al., also incorporated herein by reference, discloses this method. While such a system resolves the take-up reel problem, it still requires separate disposal of the cover tape, and the cover tape must still be started with a measure of the cover tape being routed through the feeder to the pinch rollers and through the pinch rollers each and every time a new reel of component tape is started or restarted in the feeder.
Another method is disclosed in U.S. Pat. No. 4,820,369 to Masahiro et al. wherein the tape is slit using a tongue or shoe that slides under cover tape to cut and peel the tape back along an edge or center cut. A similar disclosure by Siemens in DE 3214600A1 teaches a peeling back operation. However, it will be appreciated that various peeling and cutting operations, in close proximity to a pick-up location must be highly reliable. Moreover, when a cutting edge is employed the edge will, over time, become dulled by the cutting become an obstacle to forward motion of the carrier tapexe2x80x94possibly resulting in a jam and loss of productivity, and/or replacement that will require that the feeder be removed from service.
The present invention solves the various problems described above by not only avoiding the complete separation of the carrier tape and the cover tape and allowing disposal of the cover tape and carrier base, but also avoiding the need for a sharp cutting edge through the use of a radiant energy beam or resistive thermal energy source to cut the cover tape prior to opening the tape for access to the components therebelow. More specifically, the cover tape is cut using a localized heating means such as a laser or resistive thermal energy source to vaporize a small line in parallel with the longitudinal edge of the tape. The line may be at or near an edge, or down the middle of the cover-tape layer (e.g., for wider component tapes). The cover tape flap(s) created by the laser cutting operation may then be either folded back away from the region above the component, whereby the component is exposed for retrieval at the pick-up location, or the cut may be sufficient to allow a pick head to pass through the cut, engage the component and remove it from the carrier tape depression without significant interference from the cover tape layer. Subsequent to the pick-up location, the carrier tape with the parted cover tape flap(s) still attached thereto, is then directed to a waste receptacle or similar disposal mechanism, avoiding the need for a separate cover tape take-up reel and cover tape removal.
In accordance with the present invention, there is provided a component feeding apparatus for supplying components to an automated assembly system, said system using a component feeding means having a length of component carrier tape with a plurality of regularly spaced depressions in the carrier layer, each depression holding a component therein, and a cover tape thereover to retain the components within each depression until the component approaches a pick-up location, comprising: means for applying thermal energy to a localized region of the cover layer and thereby placing a cut in the cover layer as it is advanced so as to partially expose the component and create a flap of cover layer while keeping at least one edge of said cover layer affixed to the component carrier tape; and means for contacting the component through the cut and removing the component from the depression.
In accordance with another aspect of the present invention there is provided, in a component feeding apparatus for supplying components to an automated system for assembling printed circuit boards, said system using a component feeding apparatus having a length of component carrier tape with a plurality of regularly spaced depressions, each depression holding a component therein, and a cover tape layer thereover to retain the components within each depression until the component approaches a pick-up location, a method of presenting components for retrieval at the pick-up location, comprising the steps of: in advance of the pick-up location, cutting the cover layer with a thermal energy source so as to create a cover layer flap and thereby partially expose the component while keeping at least one edge of said cover layer affixed to the component carrier tape; and while feeding the component carrier tape, guiding the cover layer flap around the pick-up location, whereby the component is exposed and the cover layer flap will not prevent retrieval of the component at the pick-up location.
The techniques described above are advantageous because they simplify the component feeders used with surface mount assembly operations. By eliminating the need to separately handle the carrier and cover tape members, and the need to sharpen or replace cutting edges, the component feeding process is simplified and made more reliable. Moreover, once the cover tape problem is appropriately addressed, it may be easier to utilize a splicing operation wherein the end of one reel of component tape can be spliced to the beginning of another reel, and the operation of the assembly system can proceed uninterrupted for longer periods of time.
The aspects of the present invention are advantageous because they provide a reliable cutting technique that is useful for cutting a cover tape, and techniques for spacing or positioning the radiant energy beam or resistive thermal energy source for optimized cutting. A wide variety of component feeding operations can be implemented using these techniques. Each technique can ensure that the component tape (carrier and cover) is fed to the pick-up location with a slit cover tape, thereby simplifying access to the components and disposal of the component tape. As a result of the invention, the performance and maintenance of a component tape feeding system is significantly improved.